Ejector cycle systems provided with multiple evaporators have been conventionally known as in JP Patent No. 3322263 (corresponding to U.S. Pat. No. 6,574,987, U.S. Pat. No. 6,477,857).
As illustrated in FIG. 6, a first evaporator 16 is connected downstream of an ejector 15 with respect to a refrigerant flow. An accumulator 32 that is a vapor-liquid separator is located downstream of the first evaporator 16 with respect to the refrigerant flow. Further, a second evaporator 20 is located between a liquid phase refrigerant outlet of the accumulator 32 and a refrigerant suction port 15b of the ejector 15. The two evaporators 16, 20 are simultaneously operated.
In this refrigerant cycle, a pressure drop caused by a high-speed flow of refrigerant as expanded is utilized to draw refrigerant that flows out of the second evaporator 20, and further, velocity energy of refrigerant as expanded is converted into pressure energy at a diffuser portion 15d (pressure increasing portion) to raise the refrigerant pressure (i.e., the inlet pressure of a compressor 11). Thus, power for driving the compressor 11 can be reduced, and the efficiency of cycle operation can be enhanced.
In this refrigerant cycle, heat absorbing (cooling) action can be produced from separate spaces by using the first evaporator 16 and the second evaporator 20, or it can be produced from one and the same space by the two evaporators 16, 20. Also, the interior of a vehicle compartment can be cooled by using the two evaporators 16, 20.
In this refrigerant cycle, refrigerant that flows out of a radiator 12 all passes through a nozzle portion 15a of the ejector 15. Here, the flow rate of refrigerant that passes through the nozzle portion 15a of the ejector 15 is referred to as Gnoz. This Gnoz is set to such a flow rate that the dryness of refrigerant on the outlet side of the first evaporator 16 becomes a predetermined value or below. The refrigerant depressurized through the nozzle portion 15a is mixed with the refrigerant drawn through the refrigerant suction port 15b of the ejector 15, and flows into the first evaporator 16. The refrigerant that flows out of the first evaporator 16 is separated into vapor phase refrigerant and liquid phase refrigerant in the accumulator 32.
The refrigerant suction port 15b of the ejector 15 is depressurized and thus produces sucking action. As a result, the second evaporator 20 is supplied with the liquid phase refrigerant separated in the accumulator 32. Here, the flow rate of refrigerant drawn through the refrigerant suction port 15b is referred to as Ge. The liquid phase refrigerant that flows into the second evaporator 20 is evaporated at the second evaporator 20. Therefore, most or all of the refrigerant drawn through the refrigerant suction port 15b is vapor phase refrigerant. Consequently, the flow rate Gnoz of liquid phase refrigerant substantially contributes to the cooling capacity of the first evaporator 16. Therefore, the cooling capacity of the first evaporator 16 is influenced by Gnoz.
By increasing the flow rate Ge of refrigerant drawn to the refrigerant suction port 15b of the ejector 15, the flow rate of liquid phase refrigerant that flows into the second evaporator 20 is increased. Accordingly, the cooling capacity of the second evaporator 20 can be increased without reducing the cooling capacity of the first evaporator 16, and thus the cooling capacity of the entire cycle is increased as well.
The cooling capacity of an evaporator is defined, for example, as increment in the enthalpy of refrigerant observed when the refrigerant absorbs heat from air in the evaporator. The increment in enthalpy is defined by multiplying an increment in the specific enthalpy of refrigerant per unit weight by the flow rate of the refrigerant. The cooling capacity of the entire cycle is defined as the sum Qer of increments in the enthalpy of refrigerant at the first and second evaporators 16 and 20. The cooling capacity may also be defined as the coefficient of performance (COP) obtained by dividing Qer by the power consumed by the compressor 11.
In a conventional cycle, therefore, the phenomenon illustrated in FIG. 8 takes place. That is, when the flow ratio η (η=Ge/Gnoz) is increased, the cooling capacity Qer of the entire cycle is increased as well. The flow ratio 11 is the ratio of the flow rate Ge of refrigerant drawn into the refrigerant suction port 15b of the ejector 15 to the flow rate Gnoz of refrigerant that passes through the nozzle portion 15a of the ejector 15.
When the heat load of the conventional is low, the difference between the high pressure and the low pressure of refrigerant in the cycle is reduced; therefore, the input to the ejector 15 is reduced. In this case, a problem arises in the conventional cycle. Since the refrigerant flow rate Ge depends only on the refrigerant sucking capability of the ejector 15, the following takes placed: reduction in the input to the ejector 15→reduction in the refrigerant sucking capability of the ejector 15→reduction in the flow rate of liquid phase refrigerant that flows into the second evaporator 20→reduction in flow ratio η. This results in reduction in cooling capacity Qer.
The US 2005/0178150 proposes an ejector cycle illustrated in FIG. 7. In this ejector cycle of FIG. 7, a branch passage 18 is provided between the discharge side of a radiator 12 and the refrigerant inflow port of an ejector 15. A throttling mechanism 42 that adjusts the pressure and flow rate of refrigerant and a second evaporator 20 are located in this branch passage 18. The outlet of the second evaporator 20 is connected to the refrigerant suction port 15b of the ejector 15.
The flow of refrigerant is separated upstream of the ejector 15, and the separated refrigerant is drawn into the refrigerant suction port 15b through the branch passage 18. Therefore, the branch passage 18 is in parallel relation with the ejector 15 with respect to connection. For this reason, when refrigerant is supplied to the branch passage 18, the refrigerant sucking and discharging capability of the compressor 11 can be utilized in addition to the refrigerant sucking capability of the ejector 15.
Therefore, even though the phenomenon of reduction in the input to the ejector 15 and reduction in the refrigerant sucking capability of the ejector 15 occurs, the degree of reduction in the flow rate Ge of refrigerant drawn into the refrigerant suction port 15b of the ejector 15 can be reduced more than in the conventional cycle.
In the ejector cycle proposed in the US 2005/0178150, the flow of refrigerant is separated upstream of the ejector 15. Therefore, the flow rate Gn of refrigerant that flows out of the radiator 12 is equal to the sum of the flow rate Gnoz of refrigerant that passes through the nozzle portion 15a of the ejector 15 and the flow rate of refrigerant that flows into the second evaporator 20. The flow rate of refrigerant that flows into the second evaporator 20 is equal to the flow rate Ge of refrigerant drawn into the refrigerant suction port 15b of the ejector 15.
Therefore, the relation expressed as Gn=Gnoz+Ge can be maintained. Thus, when Gnoz is reduced, Ge is increased; when Gnoz is conversely increased, Ge is reduced. Therefore, even when the cooling capacity of the first evaporator 16 is lowered, the cooling capacity of the second evaporator 20 is increased; even when the cooling capacity of the second evaporator 20 is conversely reduced, the cooling capacity of the first evaporator 16 is increased. Hence, the cooling capacity Qer of the comparison cycle illustrated in FIG. 8 is brought. That is, in the comparison cycle, a change in cooling capacity Qer for a change in flow ratio η is smaller than that in the conventional cycle, and the cooling capacity is peaked at the optimum flow ratio ηmax.
Furthermore, in an ejector cycle system where refrigerant is circulated in a refrigerant cycle using a suction force of an ejector, oil is easily stayed in an evaporator based on an operation state of the ejector. Generally, a predetermined oil circulating amount is necessary when the system is operated under a low load for a long time in order to protect a compressor.